1. Field of the Invention
The invention relates to a method for estimating damage which a semiconductor device including a chemical compound such as GaAs had suffered due to dry etching.
2. Description of the Related Art
Damage which a semiconductor has suffered throughout a depth thereof due to dry etching has conventionally been estimated with a method utilizing a capacity versus voltage property of a semiconductor (hereinafter, referred to as "C-V method"). FIG. 1 shows a device used for carrying out the C-V method. The device comprises a half-insulating GaAs substrate 1, a GaAs acting layer 6 deposited on the GaAs substrate 1, a Shottky electrode 7 composed of Al or Pd and formed on the GaAs acting layer 6, an ohmic electrode 8 formed on the GaAs acting layer 6, and a voltage supply 10 connected both to the Shottky electrode 7 and the ohmic electrode 8. The Shottky electrode 7 and the ohmic electrode 8 are formed after the GaAs acting layer 6 has been dry etched. The voltage supply 10 applies a certain voltage across the Shottky electrode 7 and the ohmic electrode 8 to thereby measure a concentration of carriers included in the GaAs acting layer 6. In the C-V method, the formation of the Shottky electrode 7 widens a surface depletion layer. For instance, when a concentration of an acting layer of a generally used GaAs FET is 1.times.10.sup.17 cm.sup.-3, the surface depletion layer has a depth of about 1000 angstroms. Accordingly, it is impossible to estimate damage that is shallower than 1000 angstroms from a surface.
Japanese Unexamined Patent Public Disclosure No. 3-126243, which was published on May 29, 1991 in Japan, has suggested a method for measuring damage which a semiconductor has suffered throughout a depth thereof due to dry etching. In this method, a damaged layer is removed by etching, and then a lifetime of excess minority carriers of a semiconductor substrate is measured by a method in which a micro wave detecting ray is conductively attenuated.
In the C-V method, charged particles are radiated over a surface of a GaAs substrate during dry etching to damage the substrate to thereby decrease the number of carriers in the vicinity of the surface, and hence a depletion layer is widened. Thus, the C-V method has a defect that it is quite difficult to measure the concentration of carriers present shallower than 1000 angstroms measuring from a surface if a concentration of an acting layer is that of a generally used GaAs FET, for instance, 2.0.times.10.sup.17 cm.sup.-3.
In the latter mentioned method suggested in Japanese Unexamined Patent Public Disclosure No. 3-126243, a damaged layer damaged due to dry etching is first removed by etching with high accuracy without a further damage, and then an oxide layer is formed on a surface on which the damaged layer used to exist. This method can provide data relating to how deep damage penetrates into a substrate. However, it is impossible by this method to estimate distribution of damage throughout a depth of a substrate. In addition, the method exhibits a problem in that the degree of damage may be changed due to the removal of a damaged layer by etching before measurement of damage, and also due to the formation of an oxide layer.